This invention relates to an overhead return piping system specifically adapted for circulating coolant/lubricant between machine tools and a filtering unit.
Machine tools used in fabricating metal parts are supplied with a coolant liquid which both prevents the tools from overheating during machining operations and carries away heat produced during the machining. Such coolant liquid quickly becomes contaminated with metal chips and must be discharged from the machine tool and replaced with fresh coolant.
In the past, used coolant has been ejected from the machine tools into open troughs which lead to a sump in which the coolant is collected. The collected coolant is then pumped to a filtering apparatus, such as a vacuum belt filter, where metal chips and other contaminants are filtered out. After filtration, the clean coolant can be recirculated to the machine tools.
The use of in floor gravity flumes to collect used coolant, however, is subject to a number of disadvantages. In floor troughs prohibit flexibility to relocate machines. In addition, an extensive amount of civil engineering work is required during the installation phase of the flumes. Some in floor flumes can be as much as 10 feet deep, which requires extensive excavation and construction. All in floor flumes are confined spaces which are difficult to properly maintain. Finally, leaks in such in floor flumes due to poor workmanship can create significant environmental problems.
More space saving arrangements utilizing overhead return lines have also been attempted. One example of such an arrangement is disclosed in Maier, U.S. Pat. No. 5,223,156. In this arrangement, used coolant is discharged to a tank adjacent each machine tool and then pumped to one or more elevated tanks, from where it flows under the influence of gravity through an overhead return line to a collecting tank. The coolant may then be pumped from the collecting tank through a filter and recirculated to the machine tools. By means of a valve on the return line, the coolant flow to the collecting tank may be effected either continuously or intermittently. Intermittent flow achieves a kind of flushing effect which assists in removing metal chips that settle out of the used coolant. However, even with intermittent flow operation, the gravity flow is often insufficient to prevent deposition of chips from the used coolant in the overhead return line.
To prevent or remove such deposits, flushing nozzles have been installed along the overhead return line. Additional coolant can then be pumped through these nozzles in order to flush out the line. Although the use of such flushing nozzles alleviates the chip deposition problem at least to some extent, such systems can greatly increase the amount of coolant which must be circulated within the system, as well as significantly increase the overall piping complexity of the system, with consequent increases in investment and operating costs and decreases in economic efficiency.